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Infall of gas as the formation mechanism of stars up to 20 times more massive than the Sun

Abstract

Theory predicts and observations confirm that low-mass stars (like the Sun) in their early life grow by accreting gas from the surrounding material. But for stars ∼10 times more massive than the Sun (∼10M⊙), the powerful stellar radiation is expected to inhibit accretion1 and thus limit the growth of their mass. Clearly, stars with masses >10M⊙ exist, so there must be a way for them to form. The problem may be solved by non-spherical accretion2,3, which allows some of the stellar photons to escape along the symmetry axis where the density is lower. The recent detection of rotating disks5,4,6 and toroids7 around very young massive stars has lent support to the idea that high-mass (≳8M⊙) stars could form in this way. Here we report observations of an ammonia line towards a high-mass star forming region. We conclude that the gas is falling inwards towards a very young star of ∼20M⊙, in line with theoretical predictions of non-spherical accretion.

Editorial Summary

Stars in the making

High-mass or OB-type stars can dominate the appearance and evolution of galaxies and certainly synthesize heavy elements and influence the interstellar medium via energetic winds and supernovae. But current models of star formation cannot explain their existence. Low-mass stars grow initially by accreting gas from the surrounding material. But for a star 10 times more massive than the Sun, the powerful stellar radiation is expected to inhibit accretion and limit the growth of its mass. The observation of an ammonia line towards a high-mass star forming region now provides support for the theory that high-mass stars form via nonspherical accretion: gas appears to be falling inwards towards a very young star of about 20 times the mass of the Sun.